For various medical reasons, such as evaluating the histology and/or pathology of a tissue, it is often necessary for a physician to obtain a sample of a patient's body tissue. In particular, bone marrow is frequently retrieved to study its cellularity and potential infiltration with abnormal cells. The currently available procedures and instruments used for obtaining bone marrow biopsy samples, while not overly complex, almost universally result in excessive patient discomfort and often recover inadequate quantities of biopsy material which sometimes is distorted and/or difficult to interpret. In the standard bone marrow procurement protocol, using currently available instruments, (such as those disclosed in U.S. Pat. No. 4,262,676 to Khosrow Jainshidi), the patient is prepared with a suitable local anesthetic at the posterior superior iliac crest/spine. Then, a relatively narrow needle is inserted to obtain an aspirate of liquid bone marrow material to make slides for examination of cellular morphology and to evaluate the surface immunophenotype of the bone marrow cells with flow cytometry. This portion of the procedure, referred to as the bone marrow aspiration, is generally relatively less painful than the bone marrow biopsy procedure using a conventional biopsy needle. Using newer bone marrow biopsy needles which actively capture specimens, and minimize manipulation of the needle after insertion, the aspirate procedure appears to be more painful than the biopsy procedure.
After the aspirate is obtained, if necessary, a biopsy of the bone marrow is taken. A significantly wider bore needle having an inner diameter that will accommodate a suitable marrow sample is prepared with an inner stylet that extends beyond the distal end of the outer needle. The stylet's distal end may be cut at an angle, with the leading edge sufficiently sharp to pierce tissue and bone. With the stylet in place within the outer needle, the needle is pushed through the outer layers of skin and subcutaneous tissue until the needle tip reaches the surface of the cortical bone. The needle and stylet are then pushed into and through the cortical layer until the tip has penetrated into the bone marrow space.
The stylet is then removed from the proximal end of the needle, which opens up the core of the needle to accommodate entry of bone marrow material for collection and retrieval. The needle is then usually advanced another 1 to 2 centimeters at minimum with a slight twisting motion. Often, the distal end of the needle will also be provided with an angled cut and sharpened leading edge or scalloped serrations to facilitate cutting and coring the tissue. By providing a slight twisting motion as the needle is advanced, usually with no more than quarter or half turns, an appropriate sample is cored from the marrow tissue and enters the inner passage of the marrow needle.
At this point, the marrow biopsy sample is ready to be removed from the patient, although it is important that the biopsy remain within the needle as the needle is withdrawn to ensure recovery of the specimen. If the biopsy becomes dislodged and falls through the distal end of the biopsy needle, the specimen is irretrievably lost. The procedure is then unsuccessful and must be repeated from the beginning.
Various methods have been utilized by physicians to try to prevent the biopsy specimen from dislodging from the needle. For example, after the needle has entered the bone and fully cored a sample from the marrow, some physicians will pull the biopsy needle back a few millimeters and then advance it a few millimeters at a different angle than the first insertion. This theoretically will “cut” the biopsy piece at the tip of the needle. Other physicians attempt to dislodge or disrupt the connection between the specimen and the bone by making multiple complete clockwise and counterclockwise rotations of the biopsy needle while within the bone. Some physicians even hit the proximal end of the biopsy needle at its handle in an attempt to mechanically disrupt the connection between the specimen and the additional bone.
As can be plainly realized, these manipulations at the end of the procedure, attempts at ensuring that the specimen remains within the needle, can often produce substantial discomfort and anxiety to the patient. Sometimes when the bone marrow is very soft, as in patients with osteoporosis, almost all of these attempts are futile because the bone structure is so fragile. Conversely, sometimes when the bone marrow is very fibrotic, which occurs in patients with myelofibrotic diseases or in AIDS patients, it is difficult to dislodge the core biopsy, since the bone marrow itself is reinforced by the surrounding tissue. In those cases, the cored biopsy often remains attached to the bone and is not successfully recovered.
Other attempts at designing a more efficient and successful biopsy needle have met with little or no success, for various reasons, including the complexity of the devices. For example, U.S. Pat. No. 3,605,721 to Hallac, discloses a biopsy needle in which an inner tube has a weakened portion represented by strips extending between distal and proximal portions of the inner tube. The distal portion of the inner tube is adhered to an outer tube and will not rotate. Once a biopsy has entered the needle, the proximal portion of the inner tube is rotated, causing the strips to twist together and eventually break off. This twisting motion tends to twist the strips to the tube's center, thus hopefully keeping the biopsy piece proximal of the twisted and broken strips for later removal. This particular biopsy needle is only a disposable device, since the strips are broken or irreversibly warped by deformation during the twisting process. Another disadvantage is the lack of control over the twisting motions or the breakage of the strips. Essentially, the operator is left to twist the inner tube until resistance to that twisting is lost, indicating that the strips have severed. There is also no way of releasing the device's grip on tissue during the procedure, should any problems arise.
U.S. Pat. No. 5,074,311 to Hasson discloses a biopsy device that includes a pair of inner jaws that can be actuated within the outer needle to “bite off” any biopsy piece that has entered the needle. The disadvantages of this device include multiple small mechanical linkages and parts including pivot pins, which are extremely difficult and expensive to assemble and maintain, in addition to the greatly increased chance of mechanical failure resulting in failure to retrieve an adequate specimen.
U.S. Pat. No. 5,522,398, to Goldenberg et al., discloses a bone marrow biopsy needle; however, the patent teaches that an inner diameter B at the distal tip of the needle (as shown in FIG. 4 thereof) is substantially equal to an inner diameter C of the inner tube (as shown in FIG. 3C) so that there will be no ridge or lip within the instrument to impede tissue entering the inner lumen of the needle. However, observations over time of the performance of needles constructed in this manner indicates that such a relationship may impede specimen transit into and through the needle, and that a virtual obstruction phenomena may develop as a result of the above relationship between the two inner diameters. Compromise of specimen transit into the needle results in an inability of the specimen to move forward into the lumen of the needle. In addition, as the needle penetrates tissue, external pressures, especially those produced by dense bone, could deform or change the diameter at the needle tip (inner diameter B) or might transmit a force through the wall of the needle, marginally decreasing the diameter of the inner tube or snare (inner diameter C). These changes could dynamically alter the relationship between the inner diameters and cause a virtual obstruction, impeding specimen transit and making it difficult for the specimen to move forward into the needle.
Many soft tissue biopsy needles incorporate a recess in a central stylet/shaft into which the tissue prolapses and over which an outer tube passes in order to sever and capture specimens. However, since the recess can never encompass the full diameter of the lumen of the needle, such designs, by definition, can never recover full cores of tissue for analysis, limiting their ability to recover the most representative tissue samples. Also, the tendency for the tissue to prolapse into the recess will depend on the deformability characteristics of the tissue. Sclerotic/fibrotic components of soft tissue may make the material minimally deformable, therefore limiting the procedure's ability to capture adequate tissue samples for analysis. Needles which do not have recessed shafts and collect specimens by boring a full core of tissue have been limited by their ability to secure, sever and capture the tissue within the lumen of the needle for efficient recovery. Capturing mechanisms such as snare coils, as disclosed in U.S. Pat. No. 5,522,398, to Goldenberg et al., (incorporated herein by reference in its entirety) that sit within the lumen of needles can be incorporated into needles designed for soft tissue biopsy. Although a snare coil captures specimens by reducing its diameter, to adequately sever and recover a soft tissue specimen, which is more compressible then bony materials, the snare coil must be designed to reduce its diameter to a minimum. However, capturing coils whose geometries are reduced by alternative activation mechanics may be more efficient in reducing their diameters and displacing their capturing coils more efficiently towards the central axis of the lumen of the needle. Such internal capturing coils may find more applicability in more deformable materials such as softer tissues that require sampling for pathologic evaluation.